The invention relates in general to munitions and in particular to tube launched projectiles.
The rear or base end of projectiles are usually either flat or tapered. FIG. 1A shows a projectile 10 with an obturator or rotating band 16 and a flat base 12. FIG. 1B shows a projectile 14 with a rotating band 18 and a tapered base 20. The tapered base 20 is known as a boat tail. Boat tails, in a mechanical way, help reduce the aerodynamic drag at the base. A base bleed is another way to reduce base drag. Both boat tails and base bleeds are known.
A base bleed is a gas generator that operates similar to a rocket motor. The base bleed fills the aerodynamic void created behind the projectile with combustion gases, thereby reducing the base drag. The combustion gases of the base bleed produce, in effect, a very long boat tail. By reducing the base drag, the base bleed allows the projectile to fly further. For long distances, then, the base bleed is preferred.
However, when firing a projectile at a low angle and a low speed (i.e., short distances), the projectile needs base drag to fly correctly and to prevent it from tumbling out of control. A base bleed projectile requires a high elevation of the firing barrel with respect to the horizon. Thus, if one has a base bleed projectile, which has very low base drag, one cannot fire it at a low angle and a low speed. One can fire a boat tail projectile at a low angle and a low speed. Even though a boat tail has reduced drag compared to a flat base, the drag is sufficient to keep the projectile stable. The boat tail is preferred for short distances and the base bleed is preferred for long distances. To prepare for both short and long distances, one needs to have two sets of projectiles, boat tail projectiles for short distances and base bleed projectiles for long distances. Providing two sets of projectiles is costly.
The known Denel system can change the aerodynamic characteristics of a projectile in the field. The Denel system, however, requires a complete exchange of the base component of the projectile. This entails swapping a base bleed unit for a boat tail unit. The Denel system is inadequate because it requires a complete exchange of the base component either at the gun site or in the front lines. This type of complete exchange requires proper lighting as well as specialized equipment to properly clean and seat the components, to assure proper operation and gun safety.